1. Field of the Invention
This invention relates to fuel injection systems for internal combustion engines and more particularly to a system for a multicylinder engine having a plurality of time pulse generators incorporating means for modifying the normal operation of the system during start-up of the engine using a single temperature sensor common to all the generators.
2. Prior Art
Recent increases in the cost of fuel and government regulations limiting the permissible quantities of atmospheric pollutants in engine exhaust emissions have increased interest in fuel injection systems as alternatives to conventional carburetors for automobile engines. These fuel injection systems measure engine operating parameters such as manifold pressure and engine temperature and inject measured quantities of fuel, based on these conditions, to the engine cylinders.
My copending patent application, Ser. No. 629,443 entitled "Control Computer for Fuel Injection System" discloses a fuel injection system wherein the quantity of fuel provided to the engine is controlled by an electrically energized injector valve connected to a constant pressure fuel supply. A number of engine sensors control the duration of pulses provided to the injectors by a number of variable width pulse generators, each serving one or more cylinders. One of the sensor signals indicates that the engine is being cranked for starting. When this signal is received the operation of the pulse generators are changed from their normal operating mode. During cold start the injectors then provide enriched fuel charges necessitated by the relatively cold temperature of the fuel and engine which minimizes the vaporization of the fuel charge. At other times the engine may be started while it is relatively hot and a smaller fuel charge, more commensurate with the quantity which would be supplied during normal engine operation will suffice.
Because of the relatively extreme temperature conditions which may occur during start-up, and the need for a relatively large fuel charge, the ratio between the longest and shortest pulse duration which may be required during start-up is substantially larger than the ratio of pulse durations which may be required during normal operation. The ratio between the maximum and minimum pulse durations, over the engine temperature range, required during starting may be ten times as large as the ratio required during normal engine operation over the same temperature range.
Accordingly, some switching mechanism, triggered by the presence or absence of the starting signal, must be provided to switch the mode of operation of the pulse generators to provide two widely different pulse ranges and such circuits have been proposed for systems employing a single pulse generator for all of the injectors. An additional problem is encountered in systems of the type described in the aforesaid patent application, wherein a plurality of injector actuation circuits provide sequential outputs during the engine cycle for different cylinders. During start-up operation the pulses that these multiple generators provide will not typically overlap despite the possible long duration of the pulses, because of the very low engine speed; however, during normal engine operation at higher speeds the pulses may overlap and if the overlapping generators employ any common components, such as a single temperature sensor, cross-modulation can occur resulting in pulse durations during these overlapping periods which are different from the periods produced when only a single generator is being actuated.
One solution to the problem would be to provide separate sensors for each pulse generator, but this is an expensive, awkward alternative. The present invention is accordingly directed toward a system which uses a single temperature sensor to control a plurality of pulse generators during both starting and normal engine operation and in which isolation is provided so that cross-modulation does not occur during the actuation of two or more generators during normal operation.